Missing explicit instantiations in libstdc++ (was Re: Unreviewed

[Benjamin Kosnik]

> The V3 tests that instantiate types from the library that are
> not preinstantiated should contains *explicit* instantiations so
> that the tests work the same on targets without weak symbols.

Ok. All of the facet-named tests in 22_locale will have this problem, as 
the testsuite makes sure that non-standard types can be instantiated for 
all the standard facets, as a quality-of-implementation thing. 

Now that I think about it, for other reasons besides weak linking semantics, 
these should just be compile tests, not compile-linkage-execute 
tests.

I'll do the changes, thanks for sticking with this.

-benjamin